Pulsacoil 2000 Thermostat and Immersion Heater Replacement

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Pulsacoil 2000 Thermostat and Immersion Heater Replacement

Post  id0mrg on Wed May 03, 2017 4:05 pm

We had a problem with a sudden failure to heat water during off-peak.  The lower thermostat had tripped and was reset. Immersion heater resistance was fine and, when off-peak was simulated, voltage was present across the two immersion heater terminals.  "Kettling" noise indicated that the immersion heater was operating.  Next morning, after off-peak heating, the water was warm but not hot and soon ran cool.  Therefore we again simulated off-peak and checked the voltage across the immersion heater every 30 mins.  OK until after sometime between 1.5-2hrs there was no voltage across the immersion heater terminals.  Checking the hot water, we found it warm but not adequately hot. (Not surprising as we calculated that it should take some 4 hours to fully heat the whole tank from, say, 10 when cold to 73 deg C). The only conclusion we could reach was that the thermostat is faulty, switching off at too low a temperature (correctly set at 73 deg C).  
Now the difficulty...we can't move the thermostat to replace it so it looks like it has previously been fitted with something to cement it in place.  At the weekend we will apply a little more force to try to loosen it but may have to  drain the system and replace both the thermostat and the immersion heater.
Finally to my question! Can anyone please advise whether there is a recommended method of fixing the thermostat in place in its sheath such that it can subsequently be removed if required?  I was thinking perhaps of wrapping PTFE tape around the end next to the green controller and "plugging" it in but wonder if there is a better way?
A second question - I have read that the immersion heaters can be difficult to remove once they have been there for some time.  If we have to remove it, I will dose liberally with WD40 and use an extension to the spanner.  If this doesn't succeed, is it recommended to apply heat using a heat gun?
Most grateful for any guidance.
Best regards to all,
David Morgan

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Re: Pulsacoil 2000 Thermostat and Immersion Heater Replacement

Post  mike on Thu May 04, 2017 12:05 pm

The heater has failed at the rod stat pocket.
Be careful, if you pull the stat out it may leak.
Have a few screw drivers ready and find one to wedge in.
When heaters are removed, check unit for loose stuff at the bottom.
I prefer to loosen the heaters when full. Unit is supported more.
A few taps with a cold chisel does the job. Sometimes heat too.
Mike
MGC/H2O
Norfolk

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Re: Pulsacoil 2000 Thermostat and Immersion Heater Replacement

Post  id0mrg on Thu May 04, 2017 3:23 pm

Many thanks Mike. Will attempt replacement this weekend.
Best regards,
David

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Re: Pulsacoil 2000 Thermostat and Immersion Heater Replacement

Post  id0mrg on Sat May 06, 2017 5:07 pm

Your diagnosis was spot-on Mike!
I risked removing the thermostat first and found that there was a small weep of water from the thermostat sheath. So it was clear that we needed to replace both the thermostat and the immersion heater.
For the benefit of other readers with similar problem, I'm posting our experience of removing a difficult immersion heater. Following recommendations here and elsewhere, we attempted to slightly loosen the immersion heater while the tank was still full, adding strength to the cylinder and reducing the risk of distorting it. Again following forum advice, we tried persuading the spanner with a lump hammer rather than an extended lever. Nothing moved! So we tried heat from a paint-stripper hot-air gun. Because of the shield around the cylinder insulation, this heated the immersion heater body as much as anything else and we still could not budge the immersion heater. At this stage, we were wondering about a replacement unit. As a final attempt, we tried heat and then applied ice cubes to the immersion heater parts and, again using a lump hammer, the spanner began, slowly to turn. We loosened it until it was relatively free (slighter lump-hammer blows) but without leaking. To shorten the cylinder draining time, we attached hoses to both the heat exchanger drain and the bottom drain. As this unit is in a single story flat, we had to create a siphon and get the hoses outside through a window until well below the cylinder level. We measured the flow rate of the hosepipes to estimate the emptying time then allowed a bit more time. Then we unscrewed the immersion heater, cleaned everything, applied copper grease (Copaslip or Halfords copper grease), fitted the thermostat and remade power connections and...voila!
Again many thanks Mike for your diagnosis and advice.
Very best regards,
David.

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Re: Pulsacoil 2000 Thermostat and Immersion Heater Replacement

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